Light-resistant-color developing sheet for pressure-sensitive copying paper

ABSTRACT

A color developing sheet comprising a support and a developer layer coated thereon, said developer layer containing an alkaline substance, such as, sodium hydroxide in addition to clay, such as, acid clay and a phenol compound, such as, p-phenyl phenol. The alkaline substance increases the light resistance of a color image formed by pressure-contact of the developer sheet with a sheet which is coated with microcapsules containing a suitable mixture of couplers.

United States Patent [191 Hayashi et a1. 1

11] 3,856,553 Dec. 24, 1974 LlGHT-RESISTANT-COLOR DEVELOPING SHEET FOR PRESSURE-SENSITIVE COPYING PAPER Inventors: Takao Hayashi; Hiroharu Matsukawa; Masataka Kiritani, all

of Fujimiya, Japan Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan Filed: Oct. 29, 1973 Appl. No.: 410,574

Related U.S. Application Data Continuation-impart of Ser. No. 151,046, June 8, 1971, abandoned.

Foreign Application Priority Data June 8, 1970 Japan 45-49339 U.S. Cl. 117/362, 117/369 Int. Cl. B41c 1/06 Field of Search 117/362, 36.8, 36.9, 155 L References Cited UNITED STATES PATENTS 2,972,547 2/1961 Tien 117/362 X 3,516,845 6/1970 3,540,913 11/1970 3,634,121 [/1972 3,641,011 2/1972 Lin et a1. 117/362 X Primary Examiner-Thomas .1. Herbert, Jr. Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak [57} ABSTRACT A color developing sheet comprising a support and a developer layer coated thereon, said developer layer containing an alkaline substance, such as, sodium hydroxide in addition to clay, such as, acid clay and a phenol compound, such as, p-phenyl phenol. The alkaline substance increases the light resistance of a color image formed by pressure-contact of the developer sheet with a sheet which is coated with microcapsules containing a suitable mixture of couplers.

10 Claims, 10 Drawing Figures PATENTEU [1EE24 I974 SHEET 1 BF 2 FIG.2(

I (ll) FIG.

M S S K V D. N 1 E Q J M m NA A H MM mun Wm mmM Jf PATENTED UEEZ 4 I974 SHEET 2 BF 2 ASWQI LIGHT-RESISTANT-COLOR DEVELOPING SHEET FOR PRESSURE-SENSITIVE COPYING PAPER This application is a continuation-in-part application of our earlier filed application Ser. No. 151,046, filed June 8, 1971, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a color developing sheet for pressure-sensitive copying paper, and particularly to the improvement of a pressure-sensitive copying paper comprising a phenol compound as a color developer together.

2. Discussion of the Prior Art As known from U.S. Pat. Nos. 2,712,507, 2,730,465, 2,730,457, 3,418,250, etc.,the pressure-sensitive copying paper is produced by utilizing microcapsules containing a solution of a substantially colorless organic compound (hereinafter referred to as coupler) and an adsorbent material (hereinafter referred to as developer) which reacts with the coupler to form a distinctive color.

Developers generally used include clays, such as, attapulgite, acid clay, active clay, zeolite or bentonite, an organic compound, such as succinic acid, tannic acid or gallic acid, and a phenol resin. Recently, the use of a phenol compound has been proposed in place of the developing agent (Japanese Patent Publication No. 9309/65). However, not only when the phenol compound is used singly, but also when it is used conjointly with a clay mineral, a color image formed by reaction with a coupler, such as, crystal violet lactone and benzoyl leuco methylene blue, has only insufficient weatherability. In other words, such color image has the defeet that it is easily discolored or faded by radiation of sunlight or on being left to stand indoors.

Accordingly, an object of this invention is to provide an improved pressure-sensitive copying paper. Another object of the invention is to provide a method of improving the weatherability of a phenol compound used as a developer.

These objects of the invention can be achieved by adding an alkaline substance to a combination of clay and the phenol compound.

SUMMARY OF THE INVENTION The phenol compounds used in the present invention are phenol compounds in which the hydrogen atom bonded to the aromatic ring is substituted with at least one hydroxyl group. Therefore, the phenol compounds used in the invention are monohydric or polyhydric phenols in the strict chemical sense. As examples of monohydric phenols, in the strict chemical sense, there may be mentioned phenols such as p-cresol, pnonylphenol, p-phenol phenol, p-(p-bromophenyl) phenol, biphenyl phenol, 2,4-xylenol, 2,4-diphenyl phenol, 2-chloro-4-phenyl phenol, 2,3,5- trimethylphenol, tetramethyl phenol, p-t-butyl phenol and p-t-amyl phenol. As examples of polyhydric phenols, in the strict chemical sense, .there may be mentioned 4-phenyl pyrocatechol, o,o'-biphenol, 4,4'-bi-ocresol, a, a'-diphenyl-4,4-bi-o-cresol, biphenyl tetrol, 2,4'-methylene diphenol, methylene diresorcinol, 2,2- methylene di-p-cresol, methylene bis-(benzylphenol), p-p'-isopropylidene diphenol, methylene bis-(phenyl phenol), methylene bis-(halophenol), and 4,4- thiodiphenol.

The alkaline substances used in this invention include hydroxides and carbonates of alkali metals or alkaline earth metals, such as, sodium, potassium, lithium, calcium, magnesium or barium.

Suitable amounts of the phenol compound are 1-10 parts by weight per parts by weight of clay, and those of the alkaline substance are 0.2-30 parts by weight on the same basis.

The method of adding these compounds is not particularly limited. For instance, the alkaline substance may be added to a slurry of clay, and then the phenol compound may be added, or this order of addition may be reversed. Still, alternatively, a mixture of the phenol compound and the alkaline substance may be added to a slurry of clay. It is possible to add organic acids, inorganic acids, or ion-exchange resins to a coating solution of the developer.

When the'developer of the invention is used, its activity is enhanced by the alkaline substance, and there can be produced a pressure-sensitive copying paper which forms a color image of higher density. It must be emphasized, however, that the main purpose of using the alkaline substance is to increase the weatherability of a color image formed by adsorption to the phenol compound and clay upon reaction, and the increase in the activity of the conventional developers is of secondary significance.

A coating solution so obtained in accordance with the present invention is coated on a support such as paper either singly or in combination with microcapsules containing a coupler to be described.

The examples of the coupler are crystal violet lactone which is 3,3-bis-(pdimethylaminophenyl)-6- dimethylamino phthalide, benzoyl leuco methylene blue, malachite green lactone which is 3,3-bis-(pdimethylaminophenyl) phthalide, Rhodamine B lactam, 3-dialkylamino-7-dialkylamino fluoranes, and 3- methyl-2,2'-spirobi (benzo-[fl-chromene), which may be used either alone or in a mixture.

Generally, the color coupler of pressure-sensitive copying paper is used in the form of a mixture in order to render complete the instantaneous-coloring properties and light resistance of a colored image. For instance, the most well known combination is one of crystal violet lactone, which is a primary coupler and colors instantaneously, and benzoyl leuco methylene blue which has good light resistance. When this combined coupler is pressed in contact with the phenol compound,v crystal violet lactone colors instantaneously, but it takes a long time before benzoyl leuco methylene blue forms a color. Moreover, a colored image of crystal violet lactone fades during this time interval. Such defects have been eliminated by use of the developer of the present invention, as will be apparent from the Examples which appear later on.

Pressure sensitive copying paper which forms a black color usually contains a mixture of couplers which form various colors. According to the present invention, a complete black image can be obtained without assuming a red color in sunlight and the like.

Microcapsules containing a coupler are produced, for instance, in accordance with the method of U.S. Pat. No. 2,800,457. One specific example is as follows: Ten parts of acid-treated pigskin gelatin and 10 parts of gum arabic are dissolved in 400 parts of water at 40C. With addition of 0.2 part of Turkey red oil as an emulsifier, 40 parts of a coupler oil is emulsified in the aqueous solution. The coupler oil consists of 4 parts of chlorodiphenyl containing 2 percent of crystal violet lactone and 1.5 percent of benzoyl leuco methylene blue dissolved therein. The emulsification is stopped when the drop size of the oil is 5 microns on an average. Water at 40C is added to the emulsion to adjust the total amount to 900 parts, and stirring is continued. At this time, care should be taken not to lower the temperature of the liquid below 40C. Thereafter, percent acetic acid is added to adjust the pH of the liquid to 4.0-4.2 to cause coacervation. Stirring is further continued, and after a lapse of 20 minutes, the mixture is cooled with ice water to gel coacervate film deposited around the oil droplets. When the temperature of the liquid reaches 20 C, 7 parts of 37 percent formaldehyde is added, and at 10 C, a percent aqueous solution of sodium hydroxide is added to adjust the pH to 9. The addition of the sodium hydroxide at this time should be performed with utmost care. With continued stirring, the mixture is heated for minutes to adjust the temperature of the liquid to 50C. The microcapsules so obtained are cooled down to 30 C, and coated in an amount of 6 g/m as solids content on a base material having a unit weight of 40 g/m The foregoing procedure is applicable to the use of other couplers.

DETAILED DESCRIPTION OF THE INVENTION The invention will now be described more specifically by the following Examples which are presented for illustrative purposes.

EXAMPLE 1 Eight parts of sodium hydroxide (20%) was added to 300 parts of dispersing water, and a solution of 4 parts of p-phenyl phenol in 40 parts of methanol was added (p-phenyl phenol being dissolved as dodecasodium salt). With stirring, 100 parts of acid clay was gradually added, and then 20parts (as solids content) of a styrene-butadiene latex was added to form a coating solution which had a pH of 9.5. The coating solution was applied to a base paper having a unit weight of 40 g/m in an amount of 10 g/m calculated as solids content using a coating rod.

Comparative Example 1 One hundred parts of acid clay was gradually added to 300 parts of dispersing water with stirring. A solution of 4 parts of p-phenyl phenol in 30 parts of methanol was added gradually with stirring, and 20 parts of a styrene-butadiene rubber latex (as solids content) was added gradually with stirring to form a coating solution. The coating solution was applied to a base paper having a unit weight of 40 g/m in an amount of 10 g/m as solids content using a coating rod, and then allowed to dry.

Comparative Test A 1. Paper coated withmicrocapsules containing crystal violet lactone was superposed on each of the developer sheets obtained in Example 1 and Comparative Example 1, and a color was formed by applying a pressure of 600 Kg/cm After allowing it to stand for one hour in a dark place, the absorption spectrum curve at a wavelength in the range of 700 to 380p. was measured of each sheet. The absorption spectrum curve of the coupler after one-hour and three-hour irradiation of sunlight was also measured. The results obtained are shown in FIG. 1 attached in which [I] refers to the 'l)o11sil1y at absorption maximum after sunlight. irradiation Fresh density at absorption maximum Light resistance I00 Table 1 Light resistance value of crystal violet lactone Sheet One-hour sunlight Three-hour sunlight irradiation irradiation Example I 72.3% 66.4% Comparative Example 1 62.0% 56.0%

It is seen from the above obtained results that the light resistance of crystal violet lactone is markedly increased by adding the phenol compound and alkaline substance to acid clay.

(2) Paper coated with microcapsules containing 3- dibenzylamino-diethylamino fluorane was used, and a color was formed in the same manner as set forth in (1) above. The absorption spectrum curve of each sheet was measured, after allowing it to stand for one hour in a dark place, and also after subjecting it to irradiation of sunlight for'l hour and 3 hours respectively. The results obtained are shown in FIG. 2 in which the symbols have the same significance as set forth in (1) above. The light resistance value at absorption maximum (A of the coupler is given in Table 2.

Table 2 Light resistance value of 3-dibenzylamino- 7-diethylamino fluorane Sheet One-hour sunlight Three-hour sunlight irradiation irradiation Example I 92.8% 84.1% Comparative Example I 80.2% 76.0%

The transfer of the absorption maximum, after sunlight irradiation, is shown in Table 3 on the basis of the absorption spectrum curve shown in FIG. 2.

Table 3 Transfer of the absorption maximum A, of

3 dibenzylamino-7-diethylamino fluorane by sunlight irradiation The foregoing results demonstrate that the light resistance value at the absorption maximum k is markedly improved, and the transfer of the absorption maximum A is slight, according to the present invention. In the sheet of Example 1, a green color was retained with almost no discoloration after the three-hour sunlight irradiation, whereas the sheet of the Comparative Example turned red brown by the same irradiation.

EXAMPLE 2 Ten parts of 20 percent potassium hydroxide was added to 300 parts of dispersing water, and a solution of4 parts ofp,p'-isopropylidene diphenol in 40 parts of methanol was added. With stirring, acid clay was gradually added, and then 20 parts (as solids content) of a styrene-butadiene rubber latex was added with slow stirring to form a coating solution which had a pH of 9.8. The coating solution was applied to base paper having a unit weight of 40 g/m as solids content.

Comparative Example 2 Acid clay was gradually added to 300 parts of dispersing water with stirring. With continued stirring, a solution of 4 parts of p,p-isopropylidene diphenol in methanol was added gradually. Subsequently, 20 parts, calculated as solids content, of a styrene-butadiene rubber latex was added with slow stirring to form a coating solution. The coating solution was applied to base paper having a unit weight of 40 g/m in an amount of g/m as solids content.

Comparative Test B 1. Paper coated with microcapsules containing crystal violet lactone was superposed on each of the devel oper sheets obtained in Example 2 and Comparative Example 2, and a color was formed by applying a pres sure of 600 Kg/cm? After allowing it to stand for one hour in a dark place, the absorption spectrum curve at a wavelength in the range of 700 to 380p. was measured of each sheet. The absorption spectrum curve of the coupler after 1-hour and 3-hour irradiation of sunlight was also measured. The results are shown in FIG. 3, in which [1] refers to the sheet of Example 2, and [ll] refers to the sheet of Comparative Example 2, and the other symbols have the same significance as set forth in Comparative Test A, (1) above. The light resistance of crystal violet lactone at the absorption maximum is given in Table 4 below.

Table 4 Light Resistance value of crystal violet lactone The results obtained were similar to those in Comparative Test A.

2. A color was formed on each of the sheets obtained in Example 2 and Comparative Example 2 in the same manner as set forth in (l) above, using paper coated with microcapsules containing 3-dibenzylamino-7- diethylamino fluorane. The absorption spectrum curve was measured, after allowing the sheet to stand for one hour in a dark place, and also after subjecting it to irradiation of sunlight for one hour and three hours respectively. The results obtained are shown in FIG. 4 in which the symbols have the same significance as set 6 forth in (1) above. The light resistance of the coupler at the absorption maximum lt is given in Table 5.

Table 5 Light resistance value at the absorption maximum of 3dibenzylumino-7-diethylamino fluorane Sheet One-hour irradiation Three'ltour irradiation of sunlight of sunlight Example 2 88.171 83.57: Comparative Example 2 79.4% 74.77:

The transfer of the absorption maximum of A of the absorption spectrum curves in FIG. 4 is given in Table 6.

Table 6 Transfer of the absorption maximum A of 3-dibenzylaminoJ-diethylamin-o fluorane by sunlight irradiation M Sheet of fresh after one-hour after three-hour sunlight irradisunlight irradiation ation Example 2 610 p. 598 p. 580 .t Comparative Example 2 610a 580 y, 485 p.

The foregoing results were similar to those obtained in Comparative Test A.

EXAMPLE 3 plied to a base paper having a unit weight of 40 g/m in an amount of 10 g/m as solids content.

Comparative Test C 1. Paper coated with microcapsules containing crystal violet lactone was superposed on each of the developer sheets obtained in Example 3 and Comparative Example 1, and a color was formed by applying pressure of 600 Kg/cm The absorption spectrum curve of each sheet was measured, after allowing it to stand for one hour in a dark place, and this was designated as a fresh absorption spectrum curve. Thereafter, the absorption spectrum was also measured, after subjecting the sheet to sunlight irradiation for one hour and three hours respectively. The results obtained are shown in FIG. 5 in which [1] refers to the sheet obtained in Example 3, and [11] refers to the sheet of Comparative Example l, and the other symbols have the same significance as set forth in Comparative Test A, (l). The absorption spectrum curves of Comparative Example 1 were the same as those shown in FIG. 1. The light resistance of the coupler at the absorption maximum is given in Table 7.

Table 7 Light resistance value of crystal violet lactone It is seen from these results that by the conjoint use of sodium carbonate with the developer and the phenol compound, the light resistance of crystal violet lactone increases.

2. A color was formed in the same manner as set forth in (1) above, using paper coated with 3-dibenzylamino-7-diethylamino fluorane. The absorption spectrum curve of each sheet was measured after allowing it to stand for one hour in a dark place, and also after subjecting it to sunlight irradiation for 1 hour and 3 hours respectively. The results are shown in FIG. 6 in which the symbols have the same significance as set forth in (1) above. The light resistance of the coupler at the absorption maximum is given in Table 8.

Table 8 Light resistance value of 3-dibenzylamino-7- diethylamino fluorane at the absorption maximum Sheet One-hour sunlight Three-hour sunlight irradiation irradiation Example 3 39.0% 80.4% Comparative Example 1 80.2% 76.0%

The transfer of the absorption maximum by sunlight irradiation is given in Table 9 on the basis of the absorption spectrum curves shown in FIG. 6.

Table 9 Transfer of the absorption maximum A, of 3-dibenzylamino-7-diethylamino fluorane by sunlight irradiation A A after one-hour after three-hour Sheet A of fresh sunlight sunlight irradiation irradiation Example 3 610 u 595 a 550 u Comparative Example I 6l0'p 580 p 485 p.

sorption maximum A shows that there is very little change in color.

What is claimed is:

l. A color developing sheet for pressure-sensitive copying paper comprising a support and a developer layer coated thereon, said developer layer comprising an alkaline substance selected from the group consist ing of an alkali metal hydroxide and an alkali metal carbonate, in addition to a clay and a phenol compound in which the hydrogen atom bonded to the aromatic ring is substituted with at least one hydroxyl group,

said alkaline substance being present in an amount of from 0.2 to 30 parts by weight per parts by weight of said clay and said phenol compound being present in an amount of from 1 to 10 parts by'weight per 100 parts by weight of clay.

2. A color developing sheet according to claim 1, wherein said phenol compound is a member selected from the group consisting of p-t-butyl phenol, p-t-amyl phenol, p-cresol, p-nonylphenol, p(p-bromophenyl) phenol, biphenyl phenol, 2,4-xylenol, 2,4-diphenyl phenol, 2-chloro-4-phenyl phenol, 2,3,5-trimethyl phenol, tetramethyl phenol, 4-phenyl pyrocatechol, 0,0- biphenol, 4,4'-bi-o-cresol, a, a-diphenyl-4,4'-bi-ocresol, biphenyl tetrol, 2,4-methylene diphenol, methylene diresorcinol, 2,2-methylene di-p-cresol, methylene bis-(benzylphenol), methylene bis-(phenyl phenol), methylene bis-(halo-phenol), and 4,4- thiodiphenol.

3. A color developing sheet according to claim 1 wherein said alkaline substance is sodium hydroxide.

4. A color developing sheet according to claiml wherein said alkaline substance is potassium hydroxide.

5. A color developing sheet according to claim 1 wherein said alkaline substance is sodium carbonate.

6. A color developing sheet according to claim 1 wherein said phenol compound is p-phenyl phenol or p,p-isopropylidene diphenol.

7. A color developing sheet according to claim 1 wherein said clay is acid clay.

8. A color developing sheet according to claim 1 wherein said support is paper.

9. A color developing sheet according to claim 1 wherein said phenol compound is p-phenyl phenol.

10. A color developing sheet according to claim 1 wherein said phenol compound is selected from the group consisting of p-t-butyl phenol, p-t-amyl phenol, p-cresol, p-nonylphenol, p(p-bromophenyl) phenol, biphenyl phenol, 2,4-xylenol, 2,4-diphenyl phenol, 2- chloro-4 phenyl phenol, 2,3,5-trimethyl phenol and 

1. A COLOR DEVELOPING SHEET FOR PRESSURE-SENSITIVE COPYING PAPER COMPRISING A SUPPORT AND A DEVELOPER LAYER COATED THEREOF, SAID DEVELOPER LAYER COMPRISING AN ALKALINE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF AN ALKALI METAL HYDROXIDE AND AN ALKALI METAL CARBONATE, IN ADDITION TO A CLAY AND A PHENOL COMPOUND IN WHICH THE HYDROGEN ATOM BONDED TO THE AROMATIC RING IS SUBSTITUTED WITH AT LEAST ONE HYDROXYL GROUP, SAID ALKALINE SUBSTANCE BEING PRESENT IN AN AMOUNT OF FROM 0.2 TO 30 PART BY WEIGHT PER 100 PARTS BY WEIGHT OF SAID CLAY AND SAID PHENOL COMPOUND BEING PRESENT IN AN AMOUNT OF FROM 1 TO 10 PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OF CLAY.
 2. A COLOR DEVELOPING SHEET ACCORDING TO CLAIM 1, WHEREIN SAID PHENOL COMPOUND IS A MEMBER SELECTED FROM THE GROUP CONSISTIG OF P-T-BUTYL PHENOL, P-T-AMYL PHENOL, P-CRESOL, P-
 3. A color developing sheet according to claim 1 wherein said alkaline substance is sodium hydroxide.
 4. A color developing sheet according to claim 1 wherein said alkaline substance is potassium hydroxide.
 5. A color developing sheet according to claim 1 wherein said alkaline substance is sodium carbonate.
 6. A color developing sheet according to claim 1 wherein said phenol compound is p-phenyl phenol or p,p''-isopropylidene diphenol.
 7. A color developing sheet according to claim 1 wherein said clay is acid clay.
 8. A color developing sheet according to claim 1 wherein said support is paper.
 9. A color developing sheet according to claim 1 wherein said phenol compound is p-phenyl phenol.
 10. A color developing sheet according to claim 1 wherein said phenol compound is selected from the group consisting of p-t-butyl phenol, p-t-amyl phenol, p-cresol, p-nonylphenol, p(p-bromophenyl) phenol, biphenyl phenol, 2,4-xylenol, 2,4-diphenyl phenol, 2-chloro-4-phenyl phenol, 2,3,5-trimethyl phenol and tetramethyl phenol. 